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Sept. 7, 2011 -- A popular class of rheumatoid arthritis drugs may slightly increase skin cancer risk but not the risk of other cancers, a "reassuring" study finds.

Cimzia, Enbrel, Humira, Remicade, and Simponi all inhibit a natural protein called tumor necrosis factor alpha (TNFa). TNFa plays a major role in arthritis. It also plays a major role in protecting the body from infections and cancer.

The clinical trials that led to the drugs' approval showed no sign of increased cancer risk. But cancer takes a long time to develop. Worries remained that as time went on, a cancer risk would appear, says University of Miami rheumatologist Ozlem Pala, MD.

A 2006 report in the Journal of the American Medical Association found evidence of increased cancers and serious infections in patients taking anti-TNF drugs. But later studies failed to confirm the cancer risk.

"We are more or less sure now we won't see a really big increased risk of cancer with these medicines," Pala tells WebMD. "It is definitely better than what we were afraid of. But we still have to be really cautious about the possibility of cancer risk [in patients on TNF inhibitors]."

A recent analysis of clinical trial data found no increased cancer risk for TNF inhibitors -- except for an increased risk of skin cancer. Now a new analysis of patient follow-up data confirms these findings, study leader Xavier Mariette, MD, PhD, of the University of Paris, tells WebMD.

"We had exactly the same results. It means there was no increased risk of cancer in patients treated with TNF inhibitors compared to [other RA drugs]," Mariette tells WebMD. "It is very reassuring. But we did also observe an increased risk of non-melanoma skin cancer."

Mariette and colleagues also found a trend indicating increased risk of melanoma in patients on TNF inhibitors -- but this finding was weak and could have been due to chance.

Mariette notes that anti-TNF drugs weaken part of the the immune system. And such drugs are known to increase the risk of skin cancers, he says, so he is not surprised to find that anti-TNF drugs increase non-melanoma skin cancer risk by 45%.

"This means that doctors should be cautious with these drugs in patients with high lifetime sun exposure," he says. "But patients also should be aware that non-melanoma skin cancers are easily treatable."

Cimzia and Simponi were approved only two years ago. They were not included in the analyses of cancer risk by Mariette and previous researchers.

But Pala says that while the five current anti-TNF drugs are different from one another, any cancer or infection risk is probably common to the entire class of drugs.

The Mariette study appears in the Sept. 8 online issue of the Annals of Rheumatic Diseases.

SOURCES:Mariette, X. Annals of Rheumatic Diseases, published online Sept. 8, 2011.Bongartz, T. Journal of the American Medical Association, May 17, 2006.Askling, J. Pharmacoepidemiology and Drug Safety, February 2011.Xavier Mariette, MD, PhD, Institute for Health and Medical Research (INSERM), University of Paris.Ozlem Pala, MD, assistant professor of rheumatology, University of Miami Miller School of Medicine.